Eyepieces for use in wearable display systems

ABSTRACT

An example a head-mounted display device includes a light projector and an eyepiece. The eyepiece is arranged to receive light from the light projector and direct the light to a user during use of the wearable display system. The eyepiece includes a waveguide having an edge positioned to receive light from the display light source module and couple the light into the waveguide. The waveguide includes a first surface and a second surface opposite the first surface. The waveguide includes several different regions, each having different grating structures configured to diffract light according to different sets of grating vectors.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Patent Application No. 62/928,798, entitled “Eyepieces for Use inWearable Display Systems,” filed Oct. 31, 2019, which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to eyepieces for use in wearable display systemand methods for producing the same.

BACKGROUND

Optical imaging systems, such as wearable display systems (e.g.,wearable display headsets) can include one or more eyepieces thatpresent projected images to a user. Eyepieces can be constructed usingthin layers of one or more highly refractive materials. As examples,eyepieces can be constructed from one or more layers of highlyrefractive glass, silicon, metal, or polymer substrates.

In some cases, an eyepiece can be patterned (e.g., with one or morelight diffractive nanostructures) such that it projects an imageaccording to a particular focal depth. For an example, to a user viewinga patterned eyepiece, the projected image can appear to be a particulardistance away from the user.

Further, multiple eyepieces can be used in conjunction to project asimulated three-dimensional image. For example, multiple eyepieces—eachhaving a different pattern—can be layered one atop another, and eacheyepiece can project a different depth layer of a volumetric image.Thus, the eyepieces can collectively present the volumetric image to theuser across three-dimensions. This can be useful, for example, inpresenting the user with a “virtual reality” environment.

SUMMARY

This disclosure describes eyepieces for use in wearable display systemand methods for producing the same. One or more of the describedimplementations can be used to efficiently produce wearable displaysystems exhibiting high optical performance suitable for virtual realityapplications (e.g., wide fields of view, high light projectionefficiency, uniform image projection characteristics, etc.).

In an aspect, a head-mounted display device includes a light projectorand an eyepiece. The eyepiece is arranged to receive light from thelight projector and direct the light to a user during use of thewearable display system. The eyepiece includes a waveguide having anedge positioned to receive light from the display light source moduleand couple the light into the waveguide. The waveguide includes a firstsurface and a second surface opposite the first surface. In a firstregion of the waveguide, the second surface defines a plurality of firstgrating structures. The plurality of first grating structures isconfigured to diffract light in the first region of the waveguideaccording to a first set of one or more grating vectors. In a secondregion of the waveguide different from the first region, the secondsurface defines a plurality of second grating structures. The pluralityof second grating structures is configured to diffract light in thesecond region of the waveguide according to a second set of one or moregrating vectors different from the first set of one or more gratingvectors. In a third region of the waveguide different from the first andsecond regions, the second surface defines a plurality of third gratingstructures. The plurality of third grating structures is configured todiffract light in the third region of the waveguide according to a thirdset of one or more grating vectors different from the first set of oneor more grating vectors and the second set of one or more gratingvectors.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first surface can be an optically smoothsurface.

In some implementations, the first surface can be a substantially planarsurface.

In some implementations, the first set of one or more grating vectorscan include one or more first vectors extending in a first direction.The second set of one or more grating vectors can include one or moresecond vectors extending in a second direction different from the firstdirection.

In some implementations, the third set of one or more grating vectorscan include one or more third vectors extending in a third directiondifferent from the first direction and the second direction.

In some implementations, the plurality of first grating structures canextend along substantially an entirety of the second surface in thefirst region.

In some implementations, the plurality of second grating structures canextend along substantially an entirety of the second surface in thesecond region.

In some implementations, the plurality of third grating structures canextend along substantially an entirety of the second surface in thethird region.

In some implementations, the plurality of first grating structures candefine a periodic one-dimensional grating having a first gratingorientation.

In some implementations, the plurality of second grating structures candefine a periodic one-dimensional grating having a second gratingorientation different from the first grating orientation.

In some implementations, an angle between the first grating orientationand the second grating orientation can be between 50° and 70°.

In some implementations, a diffraction efficiency of a first subset ofthe plurality of second grating structures can be less than adiffraction efficiency of a second subset of the plurality of secondgrating structures. A distance between the first subset of the pluralityof second grating structures and the first region can be less than adistance between the second subset of the plurality of second gratingstructures and the first region.

In some implementations, the plurality of third grating structures candefine a periodic two-dimensional grating.

In some implementations, the plurality of third grating structures caninclude a diamond-shaped lattice.

In some implementations, a diffraction efficiency of the plurality ofthird grating structures at a first end of the third region can be lessthan is greater than a diffraction efficiency of the plurality of thirdgrating structures at a second end of the third region opposite thefirst end of the third region. A distance between the first end of thethird region and the first region can be less than a distance betweenthe second end of the third region and the first region.

In some implementations, the first, second, and third regions of thewaveguide can be in optical communication with one another.

In some implementations, the first, second, and third regions of thewaveguide can be integral with respect to one another.

In some implementations, the second region of the waveguide can at leastpartially enclose the third region of the waveguide.

In some implementations, the second region of the waveguide can bedisposed between the first and second regions of the waveguide.

In some implementations, the waveguide can extend in a first dimensionand in a second dimensions orthogonal to the second dimensions. A lengthof the waveguide in the first dimension can vary along the seconddimension.

In some implementations, the waveguide can be configured, duringoperation of the head-mounted display device, to receive the light atthe first region of the waveguide, and project the light from the secondsurface towards the eye of the user along at least one of the secondregion of the waveguide or the third region of the waveguide.

In some implementations, the head-mounted display can further include aframe attached to the light projector and the eyepiece. The frame can beconfigured, when worn by the user, to orient the eyepiece such that thefirst surface of the waveguide faces the eye of the user.

In another aspect, a method includes forming a waveguide having a firstsubstantially planar surface and a second surface opposite the firstsurface. Forming the waveguide includes defining a plurality of firstgrating structures on the second surface along a first region of thewaveguide. The plurality of first grating structures are configured todiffract light in the first region of the waveguide according to a firstset of one or more grating vector. Forming the waveguide also includesdefining a plurality of second grating structures on the second surfacealong a second region of the waveguide different from the first region.The plurality of second grating structures are configured to diffractlight in the second region of the waveguide according to a second set ofone or more grating vectors different from the first set of one or moregrating vectors. Forming the waveguide also includes defining aplurality of third grating structures on the second surface along athird region of the waveguide different from the first and secondregions. The plurality of third grating structures is configured todiffract incident light according to a third set of one or more gratingvectors different from the first set of one or more grating vectors andthe second set of one or more grating vectors.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the waveguide can be integrally formed.

In some implementations, at least one of the plurality of first gratingstructures, the plurality of second grating structures, or the pluralityof third grating structures can be imprinted using one or morelithography processes.

In some implementations, the method can further include installing thewaveguide in a head-mounted display device.

In another aspect, a method is performed to provide an image to a userusing a head-mounted display. The method includes coupling light into anedge of a waveguide of an eyepiece of the head-mounted display, anddiffracting, with a plurality of first grating structures on a surfaceof the waveguide, at least some of the light in the waveguide accordingto a first set of one or more grating vectors. The method also includesdiffracting, with a plurality of second grating structures on thesurface of the waveguide different from the first grating structures, atleast some of the light in the waveguide according to a second set ofone or more grating vectors. The method also includes diffracting, witha plurality of third grating structures on the surface of the waveguidedifferent from the first and second grating structures, at least some ofthe light in the waveguide according to a third set of one or moregrating vectors. The method also includes extracting at least some ofthe light diffracted by the first, second, and third grating structuresfrom the waveguide to provide the image to the user.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of a wearable display system.

FIG. 2A shows a conventional display system for simulatingthree-dimensional image data for a user.

FIG. 2B shows aspects of an approach for simulating three-dimensionalimage data using multiple depth planes.

FIGS. 3A-3C show relationships between radius of curvature and focalradius.

FIG. 4 shows an example of a waveguide stack for outputting imageinformation to a user in an AR eyepiece.

FIGS. 5 and 6 show examples of exit beams outputted by a waveguide.

FIG. 7 shows an example optical element.

FIGS. 8A-8C show example grating structures.

FIGS. 9A-9F show example light in-coupling, light propagation, and lightout-coupling regimes of an optical element.

FIG. 10 shows another example optical element.

FIG. 11 shows a plot of the simulated far-field efficiency of an exampleoptical element.

FIG. 12 shows example optical elements and a frame.

FIG. 13 is a flow chart diagrams of an example process for constructinga head-mounted display device using the optical elements and gratingstructures described herein.

FIG. 14 is a diagram of an example computer system.

DETAILED DESCRIPTION

FIG. 1 illustrates an example wearable display system 60 thatincorporates a one or more of the optical eyepieces described herein.The display system 60 includes a display or eyepiece 70, and variousmechanical and electronic modules and systems to support the functioningof that display 70. The display 70 may be coupled to a frame 80, whichis wearable by a display system user 90 and which is configured toposition the display 70 in front of the eyes of the user 90. The display70 may be considered eyewear in some embodiments. In some embodiments, aspeaker 100 is coupled to the frame 80 and is positioned adjacent theear canal of the user 90. The display system may also include one ormore microphones 110 to detect sound. The microphone 110 can allow theuser to provide inputs or commands to the system 60 (e.g., the selectionof voice menu commands, natural language questions, etc.), and/or canallow audio communication with other persons (e.g., with other users ofsimilar display systems). The microphone 110 can also collect audio datafrom the user's surroundings (e.g., sounds from the user and/orenvironment). In some embodiments, the display system may also include aperipheral sensor 120 a, which may be separate from the frame 80 andattached to the body of the user 90 (e.g., on the head, torso, anextremity, etc.). The peripheral sensor 120 a may acquire datacharacterizing the physiological state of the user 90 in someembodiments.

The display 70 is operatively coupled by a communications link 130, suchas by a wired lead or wireless connectivity, to a local data processingmodule 140 which may be mounted in a variety of configurations, such asfixedly attached to the frame 80, fixedly attached to a helmet or hatworn by the user, embedded in headphones, or removably attached to theuser 90 (e.g., in a backpack-style configuration or in a belt-couplingstyle configuration). Similarly, the sensor 120 a may be operativelycoupled by communications link 120 b (e.g., a wired lead or wirelessconnectivity) to the local processor and data module 140. The localprocessing and data module 140 may include a hardware processor, as wellas digital memory, such as non-volatile memory (e.g., flash memory or ahard disk drive), both of which may be utilized to assist in theprocessing, caching, and storage of data. The data may include data 1)captured from sensors (which may be, e.g., operatively coupled to theframe 80 or otherwise attached to the user 90), such as image capturedevices (e.g., cameras), microphones, inertial measurement units,accelerometers, compasses, GPS units, radio devices, gyros, and/or othersensors disclosed herein; and/or 2) acquired and/or processed using aremote processing module 150 and/or a remote data repository 160(including data relating to virtual content), possibly for passage tothe display 70 after such processing or retrieval. The local processingand data module 140 may be operatively coupled by communication links170, 180, such as via a wired or wireless communication links, to theremote processing module 150 and the remote data repository 160 suchthat these remote modules 150, 160 are operatively coupled to each otherand available as resources to the local processing and data module 140.In some embodiments, the local processing and data module 140 mayinclude one or more of the image capture devices, microphones, inertialmeasurement units, accelerometers, compasses, GPS units, radio devices,and/or gyros. In some other embodiments, one or more of these sensorsmay be attached to the frame 80, or may be standalone devices thatcommunicate with the local processing and data module 140 by wired orwireless communication pathways.

The remote processing module 150 may include one or more processors toanalyze and process data, such as image and audio information. In someembodiments, the remote data repository 160 may be a digital datastorage facility, which may be available through the internet or othernetworking configuration in a “cloud” resource configuration. In someembodiments, the remote data repository 160 may include one or moreremote servers, which provide information (e.g., information forgenerating augmented reality content) to the local processing and datamodule 140 and/or the remote processing module 150. In otherembodiments, all data is stored and all computations are performed inthe local processing and data module, allowing fully autonomous use froma remote module.

The perception of an image as being “three-dimensional” or “3-D” may beachieved by providing slightly different presentations of the image toeach eye of the user. FIG. 2A illustrates a conventional display systemfor simulating three-dimensional image data for a user. Two distinctimages 190, 200—one for each eye 210, 220—are output to the user. Theimages 190, 200 are spaced from the eyes 210, 220 by a distance 230along an optical or z-axis that is parallel to the line of sight of theuser. The images 190, 200 are flat and the eyes 210, 220 may focus onthe images by assuming a single accommodated state. Such 3-D displaysystems rely on the human visual system to combine the images 190, 200to provide a perception of depth and/or scale for the combined image.

However, the human visual system is complicated and providing arealistic perception of depth is challenging. For example, many users ofconventional “3-D” display systems find such systems to be uncomfortableor may not perceive a sense of depth at all. Objects may be perceived asbeing “three-dimensional” due to a combination of vergence andaccommodation. Vergence movements (e.g., rotation of the eyes so thatthe pupils move toward or away from each other to converge therespective lines of sight of the eyes to fixate upon an object) of thetwo eyes relative to each other are closely associated with focusing (or“accommodation”) of the lenses of the eyes. Under normal conditions,changing the focus of the lenses of the eyes, or accommodating the eyes,to change focus from one object to another object at a differentdistance will automatically cause a matching change in vergence to thesame distance, under a relationship known as the “accommodation-vergencereflex,” as well as pupil dilation or constriction. Likewise, undernormal conditions, a change in vergence will trigger a matching changein accommodation of lens shape and pupil size. As noted herein, manystereoscopic or “3-D” display systems display a scene using slightlydifferent presentations (and, so, slightly different images) to each eyesuch that a three-dimensional perspective is perceived by the humanvisual system. Such systems can be uncomfortable for some users,however, since they simply provide image information at a singleaccommodated state and work against the “accommodation-vergence reflex.”Display systems that provide a better match between accommodation andvergence may form more realistic and comfortable simulations ofthree-dimensional image data.

FIG. 2B illustrates aspects of an approach for simulatingthree-dimensional image data using multiple depth planes. With referenceto FIG. 2B, the eyes 210, 220 assume different accommodated states tofocus on objects at various distances on the z-axis. Consequently, aparticular accommodated state may be said to be associated with aparticular one of the illustrated depth planes 240, which has anassociated focal distance, such that objects or parts of objects in aparticular depth plane are in focus when the eye is in the accommodatedstate for that depth plane. In some embodiments, three-dimensional imagedata may be simulated by providing different presentations of an imagefor each of the eyes 210, 220, and also by providing differentpresentations of the image corresponding to multiple depth planes. Whilethe respective fields of view of the eyes 210, 220 are shown as beingseparate for clarity of illustration, they may overlap, for example, asdistance along the z-axis increases. In addition, while the depth planesare shown as being flat for ease of illustration, it will be appreciatedthat the contours of a depth plane may be curved in physical space, suchthat all features in a depth plane are in focus with the eye in aparticular accommodated state.

The distance between an object and an eye 210 or 220 may also change theamount of divergence of light from that object, as viewed by that eye.FIGS. 3A-3C illustrate relationships between distance and the divergenceof light rays. The distance between the object and the eye 210 isrepresented by, in order of decreasing distance, R1, R2, and R3. Asshown in FIGS. 3A-3C, the light rays become more divergent as distanceto the object decreases. As distance increases, the light rays becomemore collimated. Stated another way, it may be said that the light fieldproduced by a point (the object or a part of the object) has a sphericalwavefront curvature, which is a function of how far away the point isfrom the eye of the user. The curvature increases with decreasingdistance between the object and the eye 210. Consequently, at differentdepth planes, the degree of divergence of light rays is also different,with the degree of divergence increasing with decreasing distancebetween depth planes and the user's eye 210. While only a single eye 210is illustrated for clarity of illustration in FIGS. 3A-3C and otherfigures herein, it will be appreciated that the discussions regardingthe eye 210 may be applied to both eyes 210 and 220 of a user.

A highly believable simulation of perceived depth may be achieved byproviding, to the eye, different presentations of an image correspondingto each of a limited number of depth planes. The different presentationsmay be separately focused by the user's eye, thereby helping to providethe user with depth cues based on the amount of accommodation of the eyerequired to bring into focus different image features for the scenelocated on different depth planes and/or based on observing differentimage features on different depth planes being out of focus.

FIG. 4 illustrates an example of a waveguide stack for outputting imageinformation to a user in an AR eyepiece. A display system 250 includes astack of waveguides, or stacked waveguide assembly, 260 that may beutilized to provide three-dimensional perception to the eye/brain usinga plurality of waveguides 270, 280, 290, 300, 310. In some embodiments,the display system 250 is the system 60 of FIG. 1 , with FIG. 4schematically showing some parts of that system 60 in greater detail.For example, the waveguide assembly 260 may be part of the display 70 ofFIG. 1 . It will be appreciated that the display system 250 may beconsidered a light field display in some embodiments.

The waveguide assembly 260 may also include a plurality of features 320,330, 340, 350 between the waveguides. In some embodiments, the features320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280,290, 300, 310 and/or the plurality of lenses 320, 330, 340, 350 may beconfigured to send image information to the eye with various levels ofwavefront curvature or light ray divergence. Each waveguide level may beassociated with a particular depth plane and may be configured to outputimage information corresponding to that depth plane. Image injectiondevices 360, 370, 380, 390, 400 may function as a source of light forthe waveguides and may be utilized to inject image information into thewaveguides 270, 280, 290, 300, 310, each of which may be configured, asdescribed herein, to distribute incoming light across each respectivewaveguide, for output toward the eye 210. Light exits an output surface410, 420, 430, 440, 450 of each respective image injection device 360,370, 380, 390, 400 and is injected into a corresponding input surface460, 470, 480, 490, 500 of the respective waveguides 270, 280, 290, 300,310. In some embodiments, the each of the input surfaces 460, 470, 480,490, 500 may be an edge of a corresponding waveguide, or may be part ofa major surface of the corresponding waveguide (that is, one of thewaveguide surfaces directly facing the world 510 or the user's eye 210).In some embodiments, a beam of light (e.g., a collimated beam) may beinjected into each waveguide and may be replicated, such as by samplinginto beamlets by diffraction, in the waveguide and then directed towardthe eye 210 with an amount of optical power corresponding to the depthplane associated with that particular waveguide. In some embodiments, asingle one of the image injection devices 360, 370, 380, 390, 400 may beassociated with, and inject light into, a plurality (e.g., three) of thewaveguides 270, 280, 290, 300,310.

In some embodiments, the image injection devices 360, 370, 380, 390, 400are discrete displays that each produce image information for injectioninto a corresponding waveguide 270, 280, 290, 300, 310, respectively. Insome other embodiments, the image injection devices 360, 370, 380, 390,400 are the output ends of a single multiplexed display which maytransmit image information via one or more optical conduits (such asfiber optic cables) to each of the image injection devices 360, 370,380, 390, 400. It will be appreciated that the image informationprovided by the image injection devices 360, 370, 380, 390, 400 mayinclude light of different wavelengths, or colors.

In some embodiments, the light injected into the waveguides 270, 280,290, 300, 310 is provided by a light projector system 520, whichincludes a light module 530, which may include a light source or lightemitter, such as a light emitting diode (LED). The light from the lightmodule 530 may be directed to, and modulated by, a light modulator 540(e.g., a spatial light modulator), via a beamsplitter (BS) 550. Thelight modulator 540 may spatially and/or temporally change the perceivedintensity of the light injected into the waveguides 270, 280, 290, 300,310. Examples of spatial light modulators include liquid crystaldisplays (LCD), including a liquid crystal on silicon (LCOS) displays,and digital light processing (DLP) displays.

In some embodiments, the light projector system 520, or one or morecomponents thereof, may be attached to the frame 80 (FIG. 1 ). Forexample, the light projector system 520 may be part of a temporalportion (e.g., ear stem 82) of the frame 80 or disposed at an edge ofthe display 70. In some embodiments, the light module 530 may beseparate from the BS 550 and/or light modulator 540.

In some embodiments, the display system 250 may be a scanning fiberdisplay comprising one or more scanning fibers to project light invarious patterns (e.g., raster scan, spiral scan, Lissajous patterns,etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimatelyinto the eye 210 of the user. In some embodiments, the illustrated imageinjection devices 360, 370, 380, 390, 400 may schematically represent asingle scanning fiber or a bundle of scanning fibers configured toinject light into one or a plurality of the waveguides 270, 280, 290,300, 310. In some other embodiments, the illustrated image injectiondevices 360, 370, 380, 390, 400 may schematically represent a pluralityof scanning fibers or a plurality of bundles of scanning fibers, each ofwhich are configured to inject light into an associated one of thewaveguides 270, 280, 290, 300, 310. One or more optical fibers maytransmit light from the light module 530 to the one or more waveguides270, 280, 290, 300, and 310. In addition, one or more interveningoptical structures may be provided between the scanning fiber, orfibers, and the one or more waveguides 270, 280, 290, 300, 310 to, forexample, redirect light exiting the scanning fiber into the one or morewaveguides 270,280,290,300,310.

A controller 560 controls the operation of the stacked waveguideassembly 260, including operation of the image injection devices 360,370, 380, 390, 400, the light source 530, and the light modulator 540.In some embodiments, the controller 560 is part of the local dataprocessing module 140. The controller 560 includes programing (e.g.,instructions in a non-transitory medium) that regulates the timing andprovision of image information to the waveguides 270, 280, 290, 300,310. In some embodiments, the controller may be a single integraldevice, or a distributed system connected by wired or wirelesscommunication channels. The controller 560 may be part of the processingmodules 140 or 150 (FIG. 1 ) in some embodiments.

The waveguides 270, 280, 290, 300, 310 may be configured to propagatelight within each respective waveguide by total internal reflection(TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or haveanother shape (e.g., curved), with major top and bottom surfaces andedges extending between those major top and bottom surfaces. In theillustrated configuration, the waveguides 270, 280, 290, 300, 310 mayeach include out-coupling optical elements 570, 580, 590, 600, 610 thatare configured to extract light out of a waveguide by redirecting thelight, propagating within each respective waveguide, out of thewaveguide to output image information to the eye 210. Extracted lightmay also be referred to as out-coupled light and the out-couplingoptical elements light may also be referred to light extracting opticalelements. An extracted beam of light may be output by the waveguide atlocations at which the light propagating in the waveguide strikes alight extracting optical element. The out-coupling optical elements 570,580, 590, 600, 610 may be, for example, diffractive optical features,including diffractive gratings, as discussed further herein. While theout-coupling optical elements 570, 580, 590, 600, 610 are illustrated asbeing disposed at the bottom major surfaces of the waveguides 270, 280,290, 300, 310, in some embodiments they may be disposed at the topand/or bottom major surfaces, and/or may be disposed directly in thevolume of the waveguides 270, 280, 290, 300, 310. In some embodiments,the out-coupling optical elements 570, 580, 590, 600, 610 may be formedin a layer of material that is attached to a transparent substrate toform the waveguides 270, 280, 290, 300, 310. In some other embodiments,the waveguides 270, 280, 290, 300, 310 may be a monolithic piece ofmaterial and the out-coupling optical elements 570, 580, 590, 600, 610may be formed on a surface and/or in the interior of that piece ofmaterial.

Each waveguide 270, 280, 290, 300, 310 may output light to form an imagecorresponding to a particular depth plane. For example, the waveguide270 nearest the eye may deliver collimated beams of light to the eye210. The collimated beams of light may be representative of the opticalinfinity focal plane. The next waveguide up 280 may output collimatedbeams of light which pass through the first lens 350 (e.g., a negativelens) before reaching the eye 210. The first lens 350 may add a slightconvex wavefront curvature to the collimated beams so that the eye/braininterprets light coming from that waveguide 280 as originating from afirst focal plane closer inward toward the eye 210 from opticalinfinity. Similarly, the third waveguide 290 passes its output lightthrough both the first lens 350 and the second lens 340 before reachingthe eye 210. The combined optical power of the first lens 350 and thesecond lens 340 may add another incremental amount of wavefrontcurvature so that the eye/brain interprets light coming from the thirdwaveguide 290 as originating from a second focal plane that is evencloser inward from optical infinity than was light from the secondwaveguide 280.

The other waveguide layers 300, 310 and lenses 330, 320 are similarlyconfigured, with the highest waveguide 310 in the stack sending itsoutput through all of the lenses between it and the eye for an aggregatefocal power representative of the closest focal plane to the person. Tocompensate for the stack of lenses 320, 330, 340, 350 whenviewing/interpreting light coming from the world 510 on the other sideof the stacked waveguide assembly 260, a compensating lens layer 620 maybe disposed at the top of the stack to compensate for the aggregateoptical power of the lens stack 320, 330, 340, 350 below. Such aconfiguration provides as many perceived focal planes as there areavailable waveguide/lens pairings. Both the out-coupling opticalelements of the waveguides and the focusing aspects of the lenses may bestatic (i.e., not dynamic or electro-active). In some alternativeembodiments, either or both may be dynamic using electro-activefeatures.

In some embodiments, two or more of the waveguides 270, 280, 290, 300,310 may have the same associated depth plane. For example, multiplewaveguides 270, 280, 290, 300, 310 may output images set to the samedepth plane, or multiple subsets of the waveguides 270, 280, 290, 300,310 may output images set to the same plurality of depth planes, withone set for each depth plane. This can provide advantages for forming atiled image to provide an expanded field of view at those depth planes.

The out-coupling optical elements 570, 580, 590, 600, 610 may beconfigured to both redirect light out of their respective waveguides andto output this light with the appropriate amount of divergence orcollimation for a particular depth plane associated with the waveguide.As a result, waveguides having different associated depth planes mayhave different configurations of out-coupling optical elements 570, 580,590, 600, 610, which output light with a different amount of divergencedepending on the associated depth plane. In some embodiments, the lightextracting optical elements 570, 580, 590, 600, 610 may be volumetric orsurface features, which may be configured to output light at specificangles. For example, the light extracting optical elements 570, 580,590, 600, 610 may be volume holograms, surface holograms, and/ordiffraction gratings. In some embodiments, the features 320, 330, 340,350 may not be lenses; rather, they may simply be spacers (e.g.,cladding layers and/or structures for forming air gaps).

In some embodiments, the out-coupling optical elements 570, 580, 590,600, 610 are diffractive features with a diffractive efficiencysufficiently low such that only a portion of the power of the light in abeam is re-directed toward the eye 210 with each interaction, while therest continues to move through a waveguide via TIR. Accordingly, theexit pupil of the light module 530 is replicated across the waveguide tocreate a plurality of output beams carrying the image information fromlight source 530, effectively expanding the number of locations wherethe eye 210 may intercept the replicated light source exit pupil. Thesediffractive features may also have a variable diffractive efficiencyacross their geometry to improve uniformity of light output by thewaveguide.

In some embodiments, one or more diffractive features may be switchablebetween “on” states in which they actively diffract, and “off” states inwhich they do not significantly diffract. For instance, a switchablediffractive element may include a layer of polymer dispersed liquidcrystal in which microdroplets form a diffraction pattern in a hostmedium, and the refractive index of the microdroplets may be switched tosubstantially match the refractive index of the host material (in whichcase the pattern does not appreciably diffract incident light) or themicrodroplet may be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, a camera assembly 630 (e.g., a digital camera,including visible light and IR light cameras) may be provided to captureimages of the eye 210, parts of the eye 210, or at least a portion ofthe tissue surrounding the eye 210 to, for example, detect user inputs,extract biometric information from the eye, estimate and track the gazedirection of the eye, to monitor the physiological state of the user,etc. In some embodiments, the camera assembly 630 may include an imagecapture device and a light source to project light (e.g., IR or near-IRlight) to the eye, which may then be reflected by the eye and detectedby the image capture device. In some embodiments, the light sourceincludes light emitting diodes (“LEDs”), emitting in IR or near-IR. Insome embodiments, the camera assembly 630 may be attached to the frame80 (FIG. 1 ) and may be in electrical communication with the processingmodules 140 or 150, which may process image information from the cameraassembly 630 to make various determinations regarding, for example, thephysiological state of the user, the gaze direction of the wearer, irisidentification, etc. In some embodiments, one camera assembly 630 may beutilized for each eye, to separately monitor each eye.

FIG. 5 illustrates an example of exit beams output by a waveguide. Onewaveguide is illustrated (with a perspective view), but other waveguidesin the waveguide assembly 260 (FIG. 4 ) may function similarly. Light640 is injected into the waveguide 270 at the input surface 460 of thewaveguide 270 and propagates within the waveguide 270 by TIR. Throughinteraction with diffractive features, light exits the waveguide as exitbeams 650. The exit beams 650 replicate the exit pupil from a projectordevice which projects images into the waveguide. Any one of the exitbeams 650 includes a sub-portion of the total energy of the input light640. And in a perfectly efficient system, the summation of the energy inall the exit beams 650 would equal the energy of the input light 640.The exit beams 650 are illustrated as being substantially parallel inFIG. 6 but, as discussed herein, some amount of optical power may beimparted depending on the depth plane associated with the waveguide 270.Parallel exit beams may be indicative of a waveguide with out-couplingoptical elements that out-couple light to form images that appear to beset on a depth plane at a large distance (e.g., optical infinity) fromthe eye 210. Other waveguides or other sets of out-coupling opticalelements may output an exit beam pattern that is more divergent, asshown in FIG. 6 , which would require the eye 210 to accommodate to acloser distance to bring it into focus on the retina and would beinterpreted by the brain as light from a distance closer to the eye 210than optical infinity.

Additional information regarding wearable display systems (e.g.,including optical elements used in wearable display systems) can befound in U.S. patent application Ser. No. 16/221,359, filed Dec. 14,2018, and entitled “EYEPIECES FOR AUGMENTED REALITY DISPLAY SYSTEM,” thecontents of which are incorporated by reference in their entirety.

The wearable display system 60 can include one or more optical elements(e.g., waveguides), each of which has multiple different types ofgrating structures that govern the manner in which light in-couples intothe optical element, propagates through the optical element, andout-couples from the optical element. Further, the grating structurescan be defined on a single surface of the optical element (e.g., thesurface of the optical element that faces the user's eye when thewearable display system 60 is worn by the user). This is beneficial, forexample, as it enables the optical element to be produced more easily(e.g., compared to an optical element having grating structures definedon multiple different surfaces).

As an example, an eyepiece of the wearable display system 60 can beformed by one or more one or more optical elements, such as thewaveguide stack shown in FIG. 4 . Further, at least one of the opticalelements can include multiple types of grating structures defined alongits periphery (e.g., along an interface between an optical element andanother optical element, or along an interface between an opticalelement and air, such as out-coupling optical elements 570, 580, 590,600, 610). In particular, an optical element can include multipledifferent regions, each region having a different respective type ofgrating structure defined on its surface. Each type of grating structurecan cause light to in-couple into, propagate through, and/or out-couplefrom the optical element in a different manner. Further, these regionscan be spatially arranged such that light in-couples into the opticalelement, propagates through the optical element, and out-couples fromthe optical element to achieve a particular optical effect (e.g., tofacilitate projection of three-dimensional images to a user of thewearable display system 60).

FIG. 7 shows a plan view of an example optical element 700. The opticalelement 700 can be used to form an eyepiece of the wearable displaysystem 60. For example, one or more of the optical elements 700 can usedto form the waveguide stack shown in FIG. 4 . In some implementations,the optical element 700 can be arranged such that the z-direction facesthe user's eye when the wearable display system 60 is worn by the user.

The optical element 700 includes three regions 702 a-702 c, each havinga different respective type of grating structure 704 a-704 c definedalong its surface (e.g., the surface facing in the z-direction). Thesurface opposite the surface having the grating structures can beoptically smooth and/or substantially planar. In practice, the shape ofthe optical element 700 can vary. For example, as shown in FIG. 7 , theoptical element 700 can have a teardrop shape.

For ease of illustration, FIG. 7 shows the grating structures 704 a-704c as extending along a portion of the surface of their respectiveregions 702 a-702 c. However, in practice, one or more of the gratingstructures 704 a-704 c can be defined along an entirety or substantiallyan entirety of the surface of their respective regions 702 a-702 c. Forexample, the grating structures 704 a can extend along an entirety orsubstantially an entirety of the surface of the region 702 a. As anotherexample, the grating structures 704 b can extend along an entirety orsubstantially an entirety of the surface of the region 702 b. As anotherexample, the grating structures 704 c can extend along an entirety orsubstantially an entirety of the surface of the region 702 b. Further,for ease of illustration, the grating structures 704 a-704 c are notnecessarily drawn to scale. In practice, the dimension of each gatingstructures 704 a-704 c can differ, depending on the implementation.Additionally, each of grating structures 704 a-704 c can vary in pitch,height, material, or other characteristics within their respectiveregions 702 a-702 c as a function of position on the optical element700. For example, features of grating structures 702 b or 702 c mayincrease in height as distance from region 704 a increases.

The first region 702 a is positioned on the periphery of the opticalelement 700 (e.g., furthest along the x-direction). The second region702 b is positioned adjacent to the first region 702 a, and includes aprotrusion 706 at its interface with the first region 702 a. As shown inFIG. 7 , the protrusion 706 is defined, at its periphery, by a planaredge 708 extending in a direction 710 along the x-y plane. The direction710 is angled relative to the x-axis by an angle θ₁. In someimplementations, the angle θ₁ can be 30° or approximately 30° (e.g.,30°±10°). In some implementations, the protrusion 706 can be omitted.

The second region 702 b at least partially encloses the third region 702c. For example, as shown in FIG. 7 , the second region 702 b increasesin width (e.g., in the y-direction) as it extends in a direction awayfrom the first region 702 a (e.g., in the −x-direction), and defines aconcave shape (e.g., a reverse C-shape) that partially encloses thethird region 702 c. Further, the third region 702 c initially graduallyincreases in width (e.g., in the y-direction) as it extends in adirection away from the first region 702 a (e.g., in the −x-direction),then gradually decreases in width towards the periphery of the opticalelement 700 opposite the first region 702 a.

In some implementations, the first region 702 a, the second region 702b, and the third region 702 c can be integrally formed with one another(e.g., forming a single monolithic piece). In some implementations, atleast one of the first region 702 a, the second region 702 b, or thethird region 702 c can be formed separately from the other regions andsecured to the other regions (e.g., during a manufacturing process).

In general, a first region 702 a is configured to in-couple light intothe optical element 700 and propagate the light to the second region 702b and/or the third region 702 c. The second region 702 b and 702 c areconfigured to cause at least some light to propagate through the opticalelement 700 and cause at least some light to out-couple from the opticalelement 700. In some implementations, the first region 702 a may bereferred to as an “input coupling grating” (ICG), and the second region702 b and/or the third region 702 b may be referred to as “orthogonalpupil expanders” (OPEs) and/or “exit pupil expanders” (EPEs).

In an example usage of the optical element 700, light is injected intothe first region 702 a (e.g., using a light source, such as one or moreof the image injection devices 360, 370, 380, 390, 400). At least someof the injected light is diffracted by grating structure 704 a andpropagates internally by totally internal reflection (TIR) within theoptical element 700 from the first region 702 a into the second region702 b (e.g., in the x and/or y-directions).

Further, at least some of the light propagates internally within theoptical element 700 along the second region 702 b (e.g., orthogonally“expanding” the spatial distribution of light within the optical element700). At least some of the light within the second region 702 bpropagates internally within the optical element 700 (e.g., in thex-direction and/or y-direction) into the third region 702 c.

Similarly, at least some of the light propagates internally within theoptical element 700 along the third region 702 c (e.g., orthogonally“expanding” the spatial distribution of light within the optical element700). Further, at least some of the light within the third region 702 cis out-coupled from the optical element 700 along the third region 702 c(e.g., exiting the optical element 700 in the z-direction towards theuser's eye). Further, at least some of the light within the third region702 c propagates internally within the optical element 700 (e.g., in thex-direction and/or y-direction) back into the second region 702 b.Further, at least some of the light re-entering the second region 702 bis out-coupled from the optical element 700 along the second region 702b (e.g., exiting the optical element 700 in the z-direction towards theuser's eye).

The regions 702 a-702 c and their respective grating structures 704a-704 c can be configured such that light out-couples from the opticalelement 700 in a specific manner, such as to achieve a particularoptical effect (e.g., to facilitate projection of images to a user). Forinstance, FIGS. 8A-8C show example configurations of the gratingstructures 704 a-704 c, respectively. The grating structures 704 a-704 ccan be defined on a surface of the optical element 700 (e.g., thesurface that faces away from the user's eye when the wearable displaysystem 60 is worn by the user) along a portion of or an entirety of eachrespectively region 702 a-702 c. In alternative embodiments, the gratingstructures 704 a-704 c can be defined on the surface of the opticalelement 700 that is nearer to the user's eye.

As shown in FIG. 8A, the grating structures 704 a are arranged such thatthey define a grating vector 802. As an example, the grating structures704 a can be configured as a one-dimensional binary grating having anumber of periodically repeating protrusions 804 (e.g., protruding fromthe optical element 700 in the z-direction), separated from one anotherby a number of periodically repeating troughs 806 (e.g., recessing intothe optical element 700 in the z-direction). The grating structures 704a repeat periodically along the grating vector 802, with each protrusion804 and trough 806 extending lengthwise in a direction perpendicular tothe grating vector 802. Further, the grating vector 802 is angledrelative to the x-axis by an angle θ₂. In some implementations, theangle θ₂ can be 30° or approximately 30° (e.g., 30°±15°). Other anglesare also possible depending on the desired relative size, shape, andlocation of the various regions 702 a-702 c.

In some implementations, some or all of the grating structures 704 a canbe blazed gratings. For example, the grating structures 704 a can beformed lithographically by applying an imprinted resist material ontothe optical element 700 and/or etching the optical element 700 accordingto a particular blazing angle with respect to the surface of the opticalelement 700. Further, some or all of the grating structures 704 a can bemetalized (e.g., coated with a metallic material) to increase the amountof light that is in-coupled into the optical element 700.

In some implementations, the grating structures 704 a can have a gratingpitch (e.g., a period) of 349 nm or approximately 349 nm (e.g., 349 nm±5nm, 349 nm 10 nm, or some other range). The pitch can be adjusteddepending on the wavelength(s) of light desired to be in-coupled intothe optical element 700. Further, in some implementations, the gratingstructures 704 a can have a duty cycle (e.g., a ratio of the width ofeach protrusion in the direction of the grating vector 802 to the periodof the grating structures) of 50%±10%. In some embodiments, the dutycycle can be zero or approximately zero (e.g., for blazed gratings).

As shown in FIG. 8B, the grating structures 704 b are arranged such thatthey define grating vectors 808 (e.g., a pair of anti-parallel vectors).As an example, the grating structures 704 b can be configured as aone-dimensional binary grating having a number of periodically repeatingprotrusions 810 (e.g., protruding from the optical element 700 in thez-direction), separated from one another by a number of periodicallyrepeating troughs 812 (e.g., recessing into the optical element 700 inthe z-direction). The grating structures 704 b repeat periodically alongthe grating vectors 808, with each protrusion 810 and trough 812extending lengthwise in a direction perpendicular to the grating vectors808. Further, the grating vector 808 is angled relative to the x-axis byan angle θ₃. In some implementations, the angle θ₃ can be 90° orapproximately 90° (e.g., 90°±10°). The grating vectors 808 also can bedefined relative to the angle θ₂, the angle θ₃, and the angle θ₆, wherethe sum of angles θ₂, θ₃, and θ₆ is zero.

In some implementations, some or all of the grating structures 704 balso can be blazed gratings. For example, the grating structures 704 bcan be formed lithographically by applying an imprinted resist materialonto the optical element 700 and/or etching the optical element 700according to a particular blazing angle with respect to the surface ofthe optical element 700. Further, some or all of the grating structures704 b can be metalized (e.g., coated with a metallic material).

In some implementations, the grating structures 704 b can have a gratingpitch (e.g., a period) of 360 nm or approximately 360 nm (e.g., 360 nm±5nm, 360 nm 10 nm, or some other range). In some implementations, thegrating structures 704 b can have a duty cycle (e.g., a ratio of thewidth of each protrusion in the direction of the grating vector 808 tothe period of the grating structures) of 50% or approximately 50% (e.g.,50%±15%).

As shown in FIG. 8C, the grating structures 704 c are arranged such thatthey define three pairs of anti-parallel vectors 814 a-814 c). As anexample, the grating structures 704 c can be configured as atwo-dimensional grating having a number of periodically repeatingstructures 816 (e.g., either holes that recess into the optical element700 in the z-direction, or protrusions that extend away from the opticalelement 700 in the z-direction). The grating structures 704 c repeatperiodically according to a two-dimension lattice (e.g., adiamond-shaped lattice). For example, the grating structures 704 c caninclude rows of periodically repeating structures 816 (e.g., eitherholes or protrusions), with each row extending in the x-direction.Adjacent rows can be offset from one another, such that the structures816 of one row are positioned between the structures 816 of its adjacentrows with respect to the x-direction (e.g., a 50% offset).

The shape and dimensions of the structures 816 can vary, depending onthe implementation. As an example, some or all of the structures 816 canbe square-shaped, circle-shaped, diamond-shaped, rectangle-shaped, orhave other shape. In some implementations, different shapes can be usedconcurrently (e.g., alternating patterns of square shaped holes andrectangle-shaped holes). In some implementations, holes and protrusionscan be used concurrently (e.g., alternating patterns of holes andprotrusions). In some implementations, the dimensions of the structures816 can be square having a width of 175 nm±15 nm.

As shown in FIG. 8C, the three pairs of anti-parallel vectors 814 a-814c are angularly offset relative to one another by an angle θ₄ (e.g.,120° or approximately 120°). Further, a first pair of anti-parallelvectors 814 a is angled relative to the x-axis by an angle θ₅, a secondpair of anti-parallel vectors 814 b is angled relative to the x-axis byan angle θ₆, and a third pair of anti-parallel vectors 814 c is angledrelative to the x-axis by an angle θ₇. In some implementations, theangles θ₅ and θ₆ can be equal to or similar to the angle θ₂ (e.g., 30°or approximately 30°). In some implementations, the angle θ₇ can be 90°or approximately 90°.

In some implementations, the grating structures 704 c can be formedlithographically by applying an imprinted resist material onto theoptical element 700 and/or and etching the optical element 700 accordingto form holes and/or protrusions.

In some implementations, the grating structures 704 c can have adifferent or the same grating pitch with respect to differentdirections. For example, in the x direction, the grating structures 704c can have a grating pitch (e.g., a period) of 200 nm or approximately250 nm (e.g., 250 nm±5 nm, 250 nm±10 nm, or some other range) betweenadjacent structures. Further, in the y-direction, the grating structures704 c can have a grating pitch of 360 nm or approximately 360 nm (e.g.,360 nm±5 nm, 360 nm±10 nm, or some other range) between adjacentstructures. In some implementations, the grating pitch of the gratingstructures 704 c can be defined according to two vectors (e.g., x and yvectors) specifying the orientation of the grating in two dimensions.For example, in some implementations, the grating structure 704 c can bedefined according to an x vector of 200 nm and a y vector of 360 nm(e.g., the vector set (200 nm, −360 nm)). In some implementations, thegrating pitch of the grating structures 704 c can be similar to that ofthe grating structures 704 b, but offset by a particular angle (e.g.,60°). In some implementations, the grating structures 704 c can have aduty cycle of 50% or approximately 50% (e.g., 50%±15%).

The optical element 700 can be formed from one or more materials. As anexample, the optical element 700 can be formed from a substrate materialhaving a refractive index n>1.75 or n>1.8. This can be useful, forexample, facilitating the projection of images according to a wide fieldof view (e.g., 45°×55°). In some implementations, the optical element700 can be formed from a substrate material having a refractive index1.8<n<2.0. Optical elements formed using these types of substratematerials are suitable for projecting images according to a singlecolor. In some implementations, the optical element 700 can be formedfrom a substrate material having a refractive index n>2.3 (e.g., LiNbO₃or SiC). Optical elements formed using these types of substratematerials are suitable for projecting images according to multiplecolors concurrently (e.g., red, green, and blue).

In some implementations, the grating structures 704 a-704 c can beformed by directly etching the optical element 700 (e.g., to removematerial from the optical element 700). In some implementations, thegrating structures 704 a-704 c can be formed by depositing material ontothe optical element 700. For example, grating structures 704 a-704 c canbe formed by depositing onto the optical element 700 a resist materialhaving a different refractive index than the optical element 700 (e.g.,material having a refractive index n between 1.5 and 1.7.

In practice, the dimensions of the optical element 700 can vary,depending on the implementation. As an example, as shown in FIG. 7 , theoptical element 700 can have a length of approximately 50 cm in thex-direction, and a width of approximately 40 cm in the y-direction.Further, the optical element 700 can have a thickness (e.g., in thez-direction) between 325 μm and 1 mm. In other examples, the opticalelement can be have a different length, width, and/or thickness,depending on the application.

Further, the configuration of the optical element 700 and its gratingstructures can vary based on the wavelength of light that it is intendedto project. For example, for an optical element 700 that is configuredto project images using green light (e.g., light having a wavelength Aof 525 nm), the optical element 700 can be formed using a materialhaving a refraction index n of 2.0, and a thickness of 500 μm (e.g., inthe z-direction). Further, the optical element 700 can be formedlithographically using a resist material having a refraction index n of1.8, 1.65, or 1.53. Further, the first region 702 a can have a diameterof 1.5 mm, and have grating structures with a pitch of 349 nm and a dutycycle of 0.5 (50%) or less. Further, the second region 702 b can havegrating structures with a pitch of 360 nm and a duty cycle of 0.5 (50%).Further, the third region 702 c have grating structures withsquare-shaped holes having a length of 175 nm, and a pitch of 200 nmbetween holes in the x-direction and 360 nm between holes in they-direction. Although an example configuration is described herein, thisis merely an illustrative example. In practice, other dimensions arealso possible, depending on the application.

The arrangement of the regions 702 a-702 c and their respective gratingstructures 704 a-704 c cause light to in-couple into the optical element700, propagate through the optical element 700, and/or out-couple fromthe optical element 700 according to different regimes (e.g.,individually or concurrently in any combination). Five example regimesare shown in FIGS. 9A-9E.

As shown in FIG. 9A, according to a first regime, light is injected intothe first region 702 a of the optical element 700. Due to the gratingstructures 704 a, at least some of the injected light propagatesinternally within the optical element 700 from the first region 702 ainto the second region 702 b in a diagonally upward direction along avector “1.” Further, due to the grating structures 704 b, at least someof the light is steered such that it propagates internally within theoptical element 700 from the second region 702 b into the third region702 c in a diagonally downward direction along a vector “2.” Further,due to the grating structures 704 c, at least some of the lightout-couples from the optical element 700 from the third region 702 calong a vector “3” (e.g., in the z-direction). According to this regime,the second region 702 b functions as an OPE (e.g., as it orthogonally“expands” the spatial distribution of light within the optical element700), whereas the third region 702 c functions as an EPE (e.g., as itout-couples light from the optical element 700 toward the user's eye).

This sequence of in-coupling, propagation, and out-coupling isrepresented in k-space by the k-space diagram 900 a, where the opticalelement 700 is represented schematically by an outer circle 902, and thematerial surrounding the optical element 700 (e.g., air, or anotheroptical element) is represented by an inner circle 904. Further,different image fields of view (e.g., as light enters the waveguide,propagates within the waveguide, and ultimately exits the waveguide) arerepresented by respective rectangles positioned relative to the outercircle 902 and inner circle 904. As shown in the k-space diagram 900 a,light is injected into the optical element 700 at the first region 702a, and propagates internally within the optical element 700 to thesecond region 702 b according to a vector “1” extending from the innercircle 904 to the outer circle 902 (e.g., extending from the rectangle906 a to the rectangle 702 b). Further, at least some of the light issteered such that it propagates internally within the optical element700 from the second region 702 b into the third region 702 c accordingto a vector “2” extending within the outer circle 902 (e.g., extendingfrom the rectangle 906 b to the rectangle 906 c). Further, at least someof the light out-couples from the optical element 700 from the thirdregion 702 c according to a vector “3” extending from the outer circle902 back into to inner circle 904 (e.g., extending from the rectangle906 c to the rectangle 906 a).

As shown in FIG. 9B, according to a second regime, light is injectedinto the first region 702 a of the optical element 700. Due to thegrating structures 704 a, at least some of the injected light propagatesinternally within the optical element 700 from the first region 702 ainto the second region 702 b in a diagonally upward direction along avector “1.” Further, due to the grating structures 704 b, at least someof the light is steered such that it continues to propagate internallywithin the optical element 700 in the second region 702 b in adiagonally downward direction along a vector “2.” Further, due to thegrating structures 704 b, at least some of the light is in turn steeredsuch that it propagates internally within the optical element 700 fromthe second region 702 b into the third region 702 c in a diagonallyupward direction along a vector “3.” Further, due to the gratingstructures 704 c, at least some of the light out-couples from theoptical element 700 from the third region 702 c along a vector “4”(e.g., in the z-direction). According to this regime, the second region702 b functions as an OPE (e.g., as it orthogonally “expands” thespatial distribution of light within the optical element 700), whereasthe third region 702 c functions as an EPE (e.g., as it out-coupleslight from the optical element 700 toward the user's eye).

This sequence of in-coupling, propagation, and out-coupling isrepresented in k-space by the k-space diagram 900 b. As shown in thek-space diagram 900 b, light is injected into the optical element 700 atthe first region 702 a, and propagates internally within the opticalelement 700 to the second region 702 b according to a vector “1”extending from the inner circle 904 to the outer circle 902 (e.g.,extending from the rectangle 908 a to the rectangle 908 b). Further, atleast some of the light is steered such that it continues to propagateinternally within the optical element 700 in the second region 702 baccording to a vector “2” extending entirely within the outer circle 902(e.g., extending from the rectangle 908 b to the rectangle 908 c).Further, at least some of the light is steered such that it propagatesinternally within the optical element 700 from the second region 702 binto the third region 702 c according to a vector “3” extending entirelywithin the outer circle 902 (e.g., extending from the rectangle 908 c tothe rectangle 908 b). Further, at least some of the light out-couplesfrom the optical element 700 from the third region 702 c according to avector “4” extending from the outer circle 902 back into to inner circle904 (e.g., extending from the rectangle 908 b to the rectangle labeled908 a).

As shown in FIG. 9C, according to a third regime, light is injected intothe first region 702 a of the optical element 700. Due to the gratingstructures 704 a, at least some of the injected light propagatesinternally within the optical element 700 from the first region 702 ainto the second region 702 b in a diagonally upward direction along avector “1.” Further, due to the grating structures 704 b, at least someof the light is in turn steered such that it propagates internallywithin the optical element 700 from the second region 702 b towards thethird region 702 c in a diagonally downward direction along a vector“2.” Further, due to the grating structures 704 b and/or 702 c, at leastsome of the light is steered such that it propagates internally withinthe optical element 700 in the third region 702 c in a diagonally upwarddirection along a vector “3.” Further, due to the grating structures 704c, at least some of the light out-couples from the optical element 700from the third region 702 c along a vector “4” (e.g., in thez-direction). According to this regime, the second region 702 bfunctions as an OPE (e.g., as it orthogonally “expands” the spatialdistribution of light within the optical element 700), whereas the thirdregion 702 c functions as an EPE (e.g., as it out-couples light from theoptical element 700 toward the user's eye).

This sequence of in-coupling, propagation, and out-coupling isrepresented in k-space by the k-space diagram 900 c. As shown in thek-space diagram 900 c, light is injected into the optical element 700 atthe first region 702 a, and propagates internally within the opticalelement 700 to the second region 702 b according to a vector “1”extending from the inner circle 904 to the outer circle 902 (e.g.,extending from the rectangle 910 a to the rectangle 910 b). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 towards the third region 702 c accordingto a vector “2” extending entirely within the outer circle 902 (e.g.,extending from the rectangle 910 b to the rectangle 910 c). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 in the third region 702 c according to avector “3” extending entirely within the outer circle 902 (e.g.,extending from the rectangle 910 c to the rectangle 910 b). Further, atleast some of the light out-couples from the optical element 700 fromthe third region 702 c according to a vector “4” extending from theouter circle 902 back into to inner circle 904 (e.g., extending from therectangle 910 b to the rectangle 910 a).

As shown in FIG. 9D, according to a fourth regime, light is injectedinto the first region 702 a of the optical element 700. Due to thegrating structures 704 a, at least some of the injected light propagatesinternally within the optical element 700 from the first region 702 ainto the second region 702 b in a diagonally upward direction along avector “1.” Further, due to the grating structures 704 b, at least someof the light is in turn steered such that it propagates internallywithin the optical element 700 from the second region 702 b towards thethird region 702 c in a diagonally downward direction along a vector“2.” Further, due to the grating structures 704 b and/or 702 c, at leastsome of the light is steered such that it propagates internally withinthe optical element 700 in the third region 702 c in a diagonally upwarddirection along a vector “3.” Further, due to the grating structures 704c, at least some of the light is steered such that it propagatesinternally within the optical element 700 back towards the second region702 b in an upward direction along a vector “4.” Further, due to thegrating structures 704 b, at least some of the light out-couples fromthe optical element 700 from the second region 702 b along a vector “5”(e.g., in the z-direction). According to this regime, the second region702 b functions as an EPE (e.g., as it out-couples light from theoptical element 700 toward the user's eye), whereas the third region 702c functions as an OPE (e.g., as it orthogonally “expands” the spatialdistribution of light within the optical element 700).

This sequence of in-coupling, propagation, and out-coupling isrepresented in k-space by the k-space diagram 900 d. As shown in thek-space diagram 900 d, light is injected into the optical element 700 atthe first region 702 a, and propagates internally within the opticalelement 700 to the second region 702 b according to a vector “1”extending from the inner circle 904 to the outer circle 902 (e.g.,extending from the rectangle 912 a to the rectangle 912 b). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 towards the third region 702 c accordingto a vector “2” extending entirely within the outer circle 902 (e.g.,extending from the rectangle 912 b to the rectangle 912 c). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 in the third region 702 c according to avector “3” extending entirely within the outer circle 902 (e.g.,extending from the rectangle 912 c to the rectangle 912 b). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 back towards the second region 702 baccording to a vector “4” extending entirely within the outer circle 902(e.g., extending from the rectangle 912 b to the rectangle 912 d).Further, at least some of the light out-couples from the optical element700 from the second region 702 b according to a vector “5” extendingfrom the outer circle 902 back into to inner circle 904 (e.g., extendingfrom the rectangle 912 d to the rectangle 912 a).

As shown in FIG. 9E, according to a fifth regime, light is injected intothe first region 702 a of the optical element 700. Due to the gratingstructures 704 a, at least some of the injected light propagatesinternally within the optical element 700 from the first region 702 ainto the second region 702 b in a diagonally upward direction along avector “1.” Further, due to the grating structures 704 b, at least someof the light is in turn steered such that it propagates internallywithin the optical element 700 from the second region 702 b towards thethird region 702 c in a diagonally downward direction along a vector“2.” Further, due to the grating structures 704 c, at least some of thelight is steered such that it propagates internally within the opticalelement 700 back towards the second region 702 b in a downward directionalong a vector “3.” Further, due to the grating structures 704 b, atleast some of the light out-couples from the optical element 700 fromthe second region 702 b along a vector “4” (e.g., in the z-direction).According to this regime, the second region 702 b functions as an EPE(e.g., as it out-couples light from the optical element 700 toward theuser's eye), whereas the third region 702 c functions as an OPE (e.g.,as it orthogonally “expands” the spatial distribution of light withinthe optical element 700).

This sequence of in-coupling, propagation, and out-coupling isrepresented in k-space by the k-space diagram 900 d. As shown in thek-space diagram 900 d, light is injected into the optical element 700 atthe first region 702 a, and propagates internally within the opticalelement 700 to the second region 702 b according to a vector “1”extending from the inner circle 904 to the outer circle 902 (e.g.,extending from the rectangle 914 a to the rectangle 914 b). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 towards the third region 702 c accordingto a vector “2” extending entirely within the outer circle 902 (e.g.,extending from the rectangle 914 b to the rectangle 914 c). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 back towards the second region 702 baccording to a vector “3” extending entirely within the outer circle 902(e.g., extending from the rectangle 914 c). Further, at least some ofthe light out-couples from the optical element 700 from the secondregion 702 b according to a vector “4” extending from the outer circle902 back into to inner circle 904 (e.g., extending from the rectangle914 d to the rectangle 914 a).

As shown in FIG. 9F, according to a sixth regime, light is injected intothe first region 702 a of the optical element 700. Due to the gratingstructures 704 a, at least some of the injected light propagatesinternally within the optical element 700 from the first region 702 ainto the second region 702 b in a diagonally upward direction along avector “1.” Further, due to the grating structures 704 b, at least someof the light is in turn steered such that it propagates internallywithin the optical element 700 from the second region 702 b towards thethird region 702 c in a diagonally downward direction along a vector“2.” Further, due to the grating structures 704 c, at least some of thelight is steered such that it propagates internally within the opticalelement 700 in a diagonally upward direction along a vector “3,” whileremaining in the third region 702 c. Further, due to the gratingstructures 704 c, at least some of the light is in turn steered suchthat it propagates internally within the optical element 700 in adiagonally downward direction along a vector “4,” while remaining in thethird region 702 c. Further, due to the grating structures 704 c, atleast some of the light out-couples from the optical element 700 fromthe third region 702 c along a vector “5” (e.g., in the z-direction).According to this regime, the second region 702 b functions as an OPE(e.g., as it orthogonally “expands” the spatial distribution of lightwithin the optical element 700), whereas the third region 702 cfunctions as both an OPE (e.g., as it orthogonally “expands” the spatialdistribution of light within the optical element 700) and an EPE (e.g.,as it out-couples light from the optical element 700 toward the user'seye).

This sequence of in-coupling, propagation, and out-coupling isrepresented in k-space by the k-space diagram 900 f. As shown in thek-space diagram 900 d, light is injected into the optical element 700 atthe first region 702 a, and propagates internally within the opticalelement 700 to the second region 702 b according to a vector “1”extending from the inner circle 904 to the outer circle 902 (e.g.,extending from the rectangle 916 a to the rectangle 916 b). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 towards the third region 702 c accordingto a vector “2” extending entirely within the outer circle 902 (e.g.,extending from the rectangle 916 b to the rectangle 916 c). Further, atleast some of the light is steered such that it propagates internallywithin the optical element 700 within the third region 702 c accordingto vectors “3” and “4” extending entirely within the outer circle 902(e.g., extending from the rectangle 916 c to the rectangle 916 b, andback again). Further, at least some of the light out-couples from theoptical element 700 from the third region 702 c according to a vector“5” extending from the outer circle 902 back into to inner circle 904(e.g., extending from the rectangle 916 c to the rectangle 916 a).

Light can in-couple into the optical element 700, propagate through theoptical element 700, and/or out-couple from the optical element 700according one or more of the aforementioned regimes concurrently. Thisenables the optical element 700 to project images across a largerportion of its surface. For example, the optical element 700 can emitlight towards a user's eye from both the second region 702 b and thethird region 702 c, rather than from just the second region 702 b orthird region 702 c alone. This can be beneficial, for example, as itenables the wearable display system 60 to project images according to awider field of view than might otherwise be possible (e.g., usingtraditional optical element configurations). For instance, in someimplementations, wearable display systems 60 having eyepieces formedfrom the optical elements described herein can project images accordingto a field of view of 45°×55° or wider. In comparison, wearable displaysystems 60 having eyepieces formed from other optical elements (e.g.,traditional optical element configurations) can project images accordingto a field of view of 40°×40° or narrower.

Further, one or more of the optical elements described herein can beformed by defining grating structures a single surface of the opticalelement (e.g., the surface of the optical element that faces away fromthe user's eye when the wearable display system 60 is worn by the user).This is beneficial, for example, as it enables the optical element to beproduced more easily (e.g., compared to an optical element havinggrating structures defined on multiple different surfaces). The surfaceopposite the surface having the grating structures can be opticallysmooth and/or substantially planar.

For example, according to some other optical element configurations,grating structures are defined on opposing surfaces of an opticalelement. However, fabricating grating structures on both surfaces of anoptical element requires double-sided processing techniques (e.g.,double-sided nanoimprinting) with strict alignment and tolerances.Further, even relatively small angular misalignments can lead todegradation of optical performance (e.g., degradation in the quality ofprojected images) and/or variations between optical elements. Furtherstill, specialized tools may be required to perform a double-sidedmanufacturing process, which can increase costs and manufacturingcomplexity. In contrast, it may be more efficient and simple to formoptical elements having grating structures of a single surface. Further,the resulting optical elements may exhibit higher optical performance,and may be more consistent from element to element.

In some implementations, each of the regions of the optical element 700can include grating structures having the same diffraction efficiencyacross the region. For example, referring to FIG. 7 , the first region702 a can include grating structures 704 a having a uniform diffractionefficiency across the first region 702 a. Similarly, the second region702 b can include grating structures 704 b having a uniform diffractionefficiency across the second region 702 b, and the third region 702 ccan include grating structures 704 a having a uniform diffractionefficiency across the third region 702 c.

In some implementations, one or more of the regions of the opticalelement 700 can include grating structures with varying diffractionefficiency across the region. For example, referring to FIG. 10 , anoptical structure 1000 can include three regions 702 a-702 c (e.g., in asimilar manner as described with respect to FIG. 7 ). However, in thisexample, the second region 702 b is further divided into sub-regions1002 a-1002 d, and the third region 702 c is further divided intosub-regions 1004 a-1004 g.

The diffraction structures in each of sub-regions can have differentdiffraction efficiencies compared to those of their neighboringsub-regions. As an example, in the second region 702 b, the gratingstructures of the sub-region 1002 a can have a first diffractionefficiency, the grating structures of the sub-region 1002 b can have asecond diffraction efficiency different from the first, and the gratingstructures of the sub-regions 1002 c and 1002 d can have a thirddiffraction efficiency different from the first and the second. As anexample, in the third region 702 c, the grating structures of thesub-regions 1004 a-1004 g each can have diffraction efficienciesdifferent from those of the neighboring sub-regions. The diffractionefficiency of grating structures can be varied, for example, by varyingthe depth, duty cycle, blazing angle, and/or other physicalcharacteristics of the grating structures.

In some implementations, the diffraction efficiency of the gratingstructures of a sub-region can increase with increasing distance betweenthe sub-region and the first region 702 a (e.g., the ICG). This can bebeneficial, for example, in producing an image having a more consistentintensity across the extent of optical element. For instance, when lightis injected into the first region 702 a, more light will be presentwithin the optical element 700 in areas nearby the first region 702 a,whereas less light will be present within the optical element 700 inareas distant the first region 702 a. By increasing the diffractionefficiency of grating structures in a sub-region based on the distancebetween the sub-region and the first region 702 a, the intensity oflight that is out-coupled from each of the sub-regions will be moreconsistent across the extent to the optical element.

In some implementations, among the sub-regions 1002 a-1002 d, thegrating structures of the sub-region 1002 a can have the lowestdiffractive efficiency, followed by the grating structures of thesub-region 1002 b, and followed by the grating structures of thesub-regions 1002 c and 1002 d. In some implementations, among thesub-regions 1004 a-1002 g, the grating structures of the sub-region 1004a can have the lowest diffractive efficiency, and the grating structuresof the sub-regions 1004 b-1004 g can have successively increasingdiffractive efficiencies from the sub-region 1004 b to the sub-region1004 g.

FIG. 11 shows a plot 1100 of the simulated far-field efficiency of anexample optical element designed according to the techniques describedherein. The plot 1100 was generated using rigorous coupled-wave analysis(RCWA) and ray-tracing techniques. As shown in FIG. 11 , the opticalelement achieved an average eye-box efficiency of 2.4% when using aresist material having a refraction index n of 1.8 and substratethickness of 500 um. Further, the optical element exhibits a relativelyuniform far-field image across the whole field-of-view, with uniformityscore of 1.06 over the entire field of view, and 0.78 across 80% of thefield of view. The plot 1100 was generated without gamma correction. Ifanti-reflection coating is added to the surface of the optical elementwithout any grating structures (e.g., the surface opposite that facingthe user), the eye-box efficiency of the optical element can be furtherimproved.

One or more of the optical elements described herein can be incorporatedinto a wearable display system 60. For example, one or more of theoptical elements described herein can be used in conjunction to projectimages towards a user's eye to depict three dimensional image data.Further, the orientation of the optical elements can vary, depending onthe application. As an example, FIG. 12 shows the orientation of twooptical elements 1200 a and 1200 b secured within a frame 80. The frame80 is aligned parallel to the x-axis, and the optical elements 1200 aand 1200 b are positioned on opposite side of the frame with respect tothe x-axis. When the user wears the frame 80, the optical elements 1200a and 1200 b are positioned on respective ones of the user's eyes.Further, the optical element 1200 a includes a major axis 1202 abisecting the optical element 1200 a widthwise, and the optical element1200 b includes a major axis 1202 b bisecting the optical element 1200 bwidthwise. The major axes 1202 a and 1202 b are angled relative to thex-axis by an angle θ₈. In practice, the angle θ₈ can vary, depending onthe application. In some implementations, the angle θ₈ can be between20° and 30°.

FIG. 13 shows an example process 1300 for constructing a head-mounteddisplay device using the optical elements and grating structuresdescribed herein.

According to the process 1300, a waveguide having a first substantiallyplanar surface and a second surface opposite the first surface isformed. For instance, one or more of the optical elements describedherein (e.g., the optical elements 700, 1000, 1200 a, and/or 1200 b) canbe formed.

Forming the waveguide includes defining a plurality of first gratingstructures on the second surface along a first region of the waveguide(step 1302). The plurality of first grating structures are configured todiffract light in the first region of the waveguide according to a firstset of one or more grating vector. Examples of the first gratingstructures and the first region are shown and described, for instance,with respect to FIGS. 7, 8A, and 10 (e.g., the region 702 a and thegrating structures 704 a).

Forming the waveguide also includes defining a plurality of secondgrating structures on the second surface along a second region of thewaveguide different from the first region (step 1304). The plurality ofsecond grating structures are configured to diffract light in the secondregion of the waveguide according to a second set of one or more gratingvectors different from the first set of one or more grating vectors.Examples of the second grating structures and the second region areshown and described, for instance, with respect to FIGS. 7, 8B, and 10(e.g., the region 702 b and the grating structures 704 b).

Forming the waveguide also includes defining a plurality of thirdgrating structures on the second surface along a third region of thewaveguide different from the first and second regions (step 1306). Theplurality of third grating structures are configured to diffractincident light according to a third set of one or more grating vectorsdifferent from the first set of one or more grating vectors and thesecond set of one or more grating vectors. Examples of the third gratingstructures and the third region are shown and described, for instance,with respect to FIGS. 7, 8B, and 10 (e.g., the region 702 c and thegrating structures 704 c).

In some implementations, each of the grating structures can be definedconcurrently or substantially concurrently (e.g., imprinted using acommon mold). In some implementations, after the grating structures areimprinted, a layer of material (e.g., metal) can be coated onto at leasta portion of the waveguide.

The waveguide is installed in a head-mounted display device (step 1308).As an example, the waveguide can be used, either alone or in combinationwith one or more other waveguides, as an eyepiece in the head-mounteddisplay device.

In some implementations, the waveguide can be integrally formed (e.g.,as a single monolithic piece).

In some implementations, at least one of the plurality of first gratingstructures, the plurality of second grating structures, or the pluralityof third grating structures are imprinted using one or more lithographyprocesses. The lithography processes can include, for example, one ormore etching and/or deposition steps.

Some implementations of subject matter and operations described in thisspecification can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. For example, in someimplementations, the local processing and data module 140, the remoteprocessing module 150, and/or the remote data repository 160 can beimplemented using digital electronic circuitry, or in computer software,firmware, or hardware, or in combinations of one or more of them. Inanother example, the process 1300 shown in FIG. 1300 can be implemented,at least in part, using digital electronic circuitry, or in computersoftware, firmware, or hardware, or in combinations of one or more ofthem (e.g., as a part of an automated or computer-assisted manufacturingprocess).

Some implementations described in this specification can be implementedas one or more groups or modules of digital electronic circuitry,computer software, firmware, or hardware, or in combinations of one ormore of them. Although different modules can be used, each module neednot be distinct, and multiple modules can be implemented on the samedigital electronic circuitry, computer software, firmware, or hardware,or combination thereof.

Some implementations described in this specification can be implementedas one or more computer programs, i.e., one or more modules of computerprogram instructions, encoded on computer storage medium for executionby, or to control the operation of, data processing apparatus. Acomputer storage medium can be, or can be included in, acomputer-readable storage device, a computer-readable storage substrate,a random or serial access memory array or device, or a combination ofone or more of them. Moreover, while a computer storage medium is not apropagated signal, a computer storage medium can be a source ordestination of computer program instructions encoded in an artificiallygenerated propagated signal. The computer storage medium can also be, orbe included in, one or more separate physical components or media (e.g.,multiple CDs, disks, or other storage devices).

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, a system on a chip, or multipleones, or combinations, of the foregoing. The apparatus can includespecial purpose logic circuitry, e.g., an FPGA (field programmable gatearray) or an ASIC (application specific integrated circuit). Theapparatus can also include, in addition to hardware, code that createsan execution environment for the computer program in question, e.g.,code that constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, a cross-platform runtimeenvironment, a virtual machine, or a combination of one or more of them.The apparatus and execution environment can realize various differentcomputing model infrastructures, such as web services, distributedcomputing and grid computing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages. A computer program may, but need not, correspondto a file in a file system. A program can be stored in a portion of afile that holds other programs or data (e.g., one or more scripts storedin a markup language document), in a single file dedicated to theprogram in question, or in multiple coordinated files (e.g., files thatstore one or more modules, sub programs, or portions of code). Acomputer program can be deployed to be executed on one computer or onmultiple computers that are located at one site or distributed acrossmultiple sites and interconnected by a communication network.

Some of the processes and logic flows described in this specificationcan be performed by one or more programmable processors executing one ormore computer programs to perform actions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andprocessors of any kind of digital computer. Generally, a processor willreceive instructions and data from a read only memory or a random accessmemory or both. A computer includes a processor for performing actionsin accordance with instructions and one or more memory devices forstoring instructions and data. A computer may also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. However, a computer need nothave such devices. Devices suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices (e.g., EPROM, EEPROM, flash memory devices, and others),magnetic disks (e.g., internal hard disks, removable disks, and others),magneto optical disks, and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

To provide for interaction with a user, operations can be implemented ona computer having a display device (e.g., a monitor, or another type ofdisplay device) for displaying information to the user and a keyboardand a pointing device (e.g., a mouse, a trackball, a tablet, a touchsensitive screen, or another type of pointing device) by which the usercan provide input to the computer. Other kinds of devices can be used toprovide for interaction with a user as well; for example, feedbackprovided to the user can be any form of sensory feedback, e.g., visualfeedback, auditory feedback, or tactile feedback; and input from theuser can be received in any form, including acoustic, speech, or tactileinput. In addition, a computer can interact with a user by sendingdocuments to and receiving documents from a device that is used by theuser; for example, by sending web pages to a web browser on a user'sclient device in response to requests received from the web browser.

A computer system may include a single computing device, or multiplecomputers that operate in proximity or generally remote from each otherand typically interact through a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), an inter-network (e.g., the Internet), a networkcomprising a satellite link, and peer-to-peer networks (e.g., ad hocpeer-to-peer networks). A relationship of client and server may arise byvirtue of computer programs running on the respective computers andhaving a client-server relationship to each other.

FIG. 14 shows an example computer system 1400 that includes a processor1410, a memory 1420, a storage device 1430 and an input/output device1440. Each of the components 1410, 1420, 1430 and 1440 can beinterconnected, for example, by a system bus 1450. The processor 1410 iscapable of processing instructions for execution within the system 1400.In some implementations, the processor 1410 is a single-threadedprocessor, a multi-threaded processor, or another type of processor. Theprocessor 1410 is capable of processing instructions stored in thememory 1420 or on the storage device 1430. The memory 1420 and thestorage device 1430 can store information within the system 1400.

The input/output device 1440 provides input/output operations for thesystem 1400. In some implementations, the input/output device 1440 caninclude one or more of a network interface device, e.g., an Ethernetcard, a serial communication device, e.g., an RS-232 port, and/or awireless interface device, e.g., an 802.11 card, a 3G wireless modem, a4G wireless modem, etc. In some implementations, the input/output devicecan include driver devices configured to receive input data and sendoutput data to other input/output devices, e.g., keyboard, printer anddisplay devices 1460. In some implementations, mobile computing devices,mobile communication devices, and other devices can be used.

While this specification contains many details, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features specific to particular examples. Certainfeatures that are described in this specification in the context ofseparate implementations can also be combined. Conversely, variousfeatures that are described in the context of a single implementationcan also be implemented in multiple embodiments separately or in anysuitable subcombination.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the invention. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. A head-mounted display device comprising: a lightprojector; and an eyepiece arranged to receive light from the lightprojector and direct the light to a user during use of the wearabledisplay system, the eyepiece comprising a waveguide comprising an edgepositioned to receive light from the light projector and couple thelight into the waveguide, the waveguide comprising a first surface and asecond surface opposite the first surface, wherein in a first region ofthe waveguide, the second surface defines a plurality of first gratingstructures, the plurality of first grating structures being configuredto diffract light in the first region of the waveguide according to afirst set of one or more grating vectors; wherein in a second region ofthe waveguide different from the first region, the second surfacedefines a plurality of second grating structures, the plurality ofsecond grating structures being configured to diffract light in thesecond region of the waveguide according to a second set of one or moregrating vectors different from the first set of one or more gratingvectors; wherein in a third region of the waveguide different from thefirst and second regions, the second surface defines a plurality ofthird grating structures, the plurality of third grating structuresbeing configured to diffract light in the third region of the waveguideaccording to a third set of one or more grating vectors different fromthe first set of one or more grating vectors and the second set of oneor more grating vectors; and wherein the second region of the waveguideat least partially encloses the third region of the waveguide.
 2. Thehead-mounted display device of claim 1, wherein the first surface is anoptically smooth surface.
 3. The head-mounted display device of claim 1,wherein the first surface is a substantially planar surface.
 4. Thehead-mounted display device of claim 1, wherein the first set of one ormore grating vectors comprises one or more first vectors extending in afirst direction, and wherein the second set of one or more gratingvectors comprises one or more second vectors extending in a seconddirection different from the first direction.
 5. The head-mounteddisplay device of claim 4, wherein the third set of one or more gratingvectors comprises one or more third vectors extending in a thirddirection different from the first direction and the second direction.6. The head-mounted display device of claim 1, wherein the plurality offirst grating structures extends along substantially an entirety of thesecond surface in the first region.
 7. The head-mounted display deviceof claim 6, wherein the plurality of second grating structures extendsalong substantially an entirety of the second surface in the secondregion.
 8. The head-mounted display device of claim 7, wherein theplurality of third grating structures extends along substantially anentirety of the second surface in the third region.
 9. The head-mounteddisplay device of claim 1, wherein the plurality of first gratingstructures defines a first periodic one-dimensional grating having afirst grating orientation.
 10. The head-mounted display device of claim9, wherein the plurality of second grating structures defines a secondperiodic one-dimensional grating having a second grating orientationdifferent from the first grating orientation.
 11. The head-mounteddisplay device of claim 10, wherein an angle between the first gratingorientation and the second grating orientation is between 50° and 70°.12. The head-mounted display device of claim 10, wherein a diffractionefficiency of a first subset of the plurality of second gratingstructures is less than a diffraction efficiency of a second subset ofthe plurality of second grating structures, and wherein a distancebetween the first subset of the plurality of second grating structuresand the first region is less than a distance between the second subsetof the plurality of second grating structures and the first region. 13.The head-mounted display device of claim 10, wherein the plurality ofthird grating structures defines a periodic two-dimensional grating. 14.The head-mounted display device of claim 13, wherein the plurality ofthird grating structures comprises a diamond-shaped lattice.
 15. Thehead-mounted display device of claim 13, wherein a diffractionefficiency of the plurality of third grating structures at a first endof the third region is less than is greater than a diffractionefficiency of the plurality of third grating structures at a second endof the third region opposite the first end of the third region, whereina distance between the first end of the third region and the firstregion is less than a distance between the second end of the thirdregion and the first region.
 16. The head-mounted display of claim 1,wherein the first, second, and third regions of the waveguide are inoptical communication with one another.
 17. The head-mounted display ofclaim 1, wherein the first, second, and third regions of the waveguideare integral with respect to one another.
 18. The head-mounted displayof claim 1, wherein the second region of the waveguide is disposedbetween the first and third regions of the waveguide.
 19. Thehead-mounted display of claim 18, further comprising: a frame attachedto the light projector and the eyepiece, wherein the frame isconfigured, when worn by the user, to orient the eyepiece such that thefirst surface of the waveguide faces the eye of the user.
 20. Thehead-mounted display of claim 1, wherein the waveguide extends in afirst dimension and in a second dimensions orthogonal to the seconddimensions, and wherein a length of the waveguide in the first dimensionvaries along the second dimension.
 21. The head-mounted display of claim1, wherein the waveguide is configured, during operation of thehead-mounted display device, to receive the light at the first region ofthe waveguide, and project the light from the second surface towards theeye of the user along at least one of the second region of the waveguideor the third region of the waveguide.
 22. A method comprising: forming awaveguide having a first substantially planar surface and a secondsurface opposite the first surface, wherein forming the waveguidecomprises: defining a plurality of first grating structures on thesecond surface along a first region of the waveguide, the plurality offirst grating structures being configured to diffract light in the firstregion of the waveguide according to a first set of one or more gratingvector, defining a plurality of second grating structures on the secondsurface along a second region of the waveguide different from the firstregion, the plurality of second grating structures being configured todiffract light in the second region of the waveguide according to asecond set of one or more grating vectors different from the first setof one or more grating vectors, and defining a plurality of thirdgrating structures on the second surface along a third region of thewaveguide different from the first and second regions, the plurality ofthird grating structures being configured to diffract incident lightaccording to a third set of one or more grating vectors different fromthe first set of one or more grating vectors and the second set of oneor more grating vectors, wherein the second region of the waveguide atleast partially encloses the third region of the waveguide.
 23. Themethod of claim 22, wherein the waveguide is integrally formed.
 24. Themethod of claim 22, wherein at least one of the plurality of firstgrating structures, the plurality of second grating structures, or theplurality of third grating structures are imprinted using one or morelithography processes.
 25. The method of claim 22, further comprising:installing the waveguide in a head-mounted display device.
 26. Ahead-mounted display device comprising: a light projector; and aneyepiece arranged to receive light from the light projector and directthe light to a user during use of the wearable display system, theeyepiece comprising a waveguide comprising an edge positioned to receivelight from the light projector and couple the light into the waveguide,the waveguide comprising a first surface and a second surface oppositethe first surface, wherein in a first region of the waveguide, thesecond surface defines a plurality of first grating structures, theplurality of first grating structures being configured to diffract lightin the first region of the waveguide according to a first set of one ormore grating vectors, the plurality of first grating structures defininga first periodic one-dimensional grating having a first gratingorientation; wherein in a second region of the waveguide different fromthe first region, the second surface defines a plurality of secondgrating structures, the plurality of second grating structures beingconfigured to diffract light in the second region of the waveguideaccording to a second set of one or more grating vectors different fromthe first set of one or more grating vectors, the plurality of secondgrating structures defining a second periodic one-dimensional gratinghaving a second grating orientation different from the first gratingorientation; wherein in a third region of the waveguide different fromthe first and second regions, the second surface defines a plurality ofthird grating structures, the plurality of third grating structuresbeing configured to diffract light in the third region of the waveguideaccording to a third set of one or more grating vectors different fromthe first set of one or more grating vectors and the second set of oneor more grating vectors; wherein a diffraction efficiency of a firstsubset of the plurality of second grating structures is less than adiffraction efficiency of a second subset of the plurality of secondgrating structures; and wherein a distance between the first subset ofthe plurality of second grating structures and the first region is lessthan a distance between the second subset of the plurality of secondgrating structures and the first region.
 27. A head-mounted displaydevice comprising: a light projector; and an eyepiece arranged toreceive light from the light projector and direct the light to a userduring use of the wearable display system, the eyepiece comprising awaveguide comprising an edge positioned to receive light from the lightprojector and couple the light into the waveguide, the waveguidecomprising a first surface and a second surface opposite the firstsurface, wherein in a first region of the waveguide, the second surfacedefines a plurality of first grating structures, the plurality of firstgrating structures being configured to diffract light in the firstregion of the waveguide according to a first set of one or more gratingvectors, the plurality of first grating structures defining a firstperiodic one-dimensional grating having a first grating orientation;wherein in a second region of the waveguide different from the firstregion, the second surface defines a plurality of second gratingstructures, the plurality of second grating structures being configuredto diffract light in the second region of the waveguide according to asecond set of one or more grating vectors different from the first setof one or more grating vectors, the plurality of second gratingstructures defining a second periodic one-dimensional grating having asecond grating orientation different from the first grating orientation;wherein in a third region of the waveguide different from the first andsecond regions, the second surface defines a plurality of third gratingstructures, the plurality of third grating structures being configuredto diffract light in the third region of the waveguide according to athird set of one or more grating vectors different from the first set ofone or more grating vectors and the second set of one or more gratingvectors, the plurality of third grating structures defining a periodictwo-dimensional grating; wherein a diffraction efficiency of theplurality of third grating structures at a first end of the third regionis less than is greater than a diffraction efficiency of the pluralityof third grating structures at a second end of the third region oppositethe first end of the third region, wherein a distance between the firstend of the third region and the first region is less than a distancebetween the second end of the third region and the first region.